1. Field of the Invention
This invention relates to airless spray equipment and more particularly to a safety nozzle assembly for airless spray pistols.
2. Prior Art
Airless paint spray pistols having a pistol-like body member with pumped fluid passageways therethrough which terminate in a forwardly directed nozzle and which utilize a trigger controlled valve assembly for controlling passage of the pumped fluid to the nozzle are known to the art. Such spray pistols normally have a nozzle tip attached at the discharged end by fastening means such as a tip nut with the tip projecting beyond the end of the tip nut. The tip terminates in an axial end face which has a nozzle orifice therethrough communicating to the internal passageways in the spray pistol body. In most instances the nozzle orifice is slot-like, or designed to produce a fan spray pattern downstream of the orifice having substantially an oval cross-section. Examples of such prior art spray pistols may be found in U.S. Pat. No. 3,743,188 issued July 3, 1973 to J. Wagner; U.S. Pat. No. 3,836,082 issued Sept. 17, 1974 to Krohn; U.S. Pat. No. 3,844,487 issued Oct. 29, 1974 to Malec and U.S. Pat. No. 2,969,926 issued Jan. 31, 1961 to Peeps. Such patents reflect, generally, the standard types of prior art airless paint spray pistols.
Airless spray pistols have one common feature. Because they are airless units, only paint or other pumped fluid exits the nozzle. In order to move the pumped fluid at a sufficient volume, extremely high pressures are utilized. In fact, it has been known to use operating pressures between 3,300-3,600 pounds per square inch and theoretical maximum pressures on the order of 6,000 p.s.i. have been envisioned although for normal nozzle sizes the usual operating pressure range is between 900 and 2900 p.s.i. These pressures still exceed those found in prior art non-airless spray pistols.
Because such high pressures are used, the pressure-mass-velocity of the pumped fluid through the nozzle orifice is extremely high and the exiting stream can, in some instances, penetrate human flesh when the flesh is positioned closely adjacent the nozzle orifice. When such penetration occurs, the fluid injected through the flesh will spread out along the underlying muscle layer, and, especially when the fluid is toxic, cause serious injury which, if not correctly treated can, at times, result in peremanent injury.
Although it is known that such flesh penetration can occur immediately adjacent the nozzle orifice, it is now determined that this is a localized phenomenon and that, because of the spreading of the spray pattern and decrease in the mass-velocity per area downstream of the nozzle, flesh injection will not occur at points remote from the nozzle opening.
It would therefore be an advance in the art to provide a safety nozzle assembly for spray pistols which would prevent injection of human flesh by the spray from the nozzle within the critical area downstream of the nozzle before the spray pattern has increased to the point at which injection cannot occur.